In the case where a predetermined rotational speed as a control command value is given to a synchronous motor so that a compressor can be driven by controlling the synchronous motor, the attempt to start driving the synchronous motor in accordance with the command value results in a large torque and may sometimes cause the desynchronization of the synchronous motor. JP-A-2003-28073 discloses a technique capable of stably starting up a compressor which has a piston and compresses refrigerant, by discharging the liquefied refrigerant out of the piston chamber.
JP-A-2006-166658 discloses a technique capable of stably starting up a gas compressor which was shut down last time with its piston at a predetermined position.
Patent Document 1: JP-A-2003-28073
Patent Document 2: JP-A-2006-166658